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softgpu: Optimize (bi-)linear texture filtering #17609

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Jun 22, 2023
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softgpu: Optimize (bi-)linear texture filtering #17609

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softgpu: Optimize (bi-)linear texture filtering 
Seeing as SampleLinearLevel is near the top in the profiler,
optimize actual bilinear filtering using SSE2. Solid win in the
synthetic benchmark (https://godbolt.org/z/fqh3xvbGx, also doubles
as correctness check), no visible difference in actual PPSSPP.
Note: profiler suggests that hot part of SampleLinearLevel is
elsewhere.
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@fp64
fp64 committed Jun 21, 2023
commit 159faaa2ec86f77c3b6606d3a18d085fce17a6a9
24 changes: 23 additions & 1 deletion GPU/Software/Sampler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -720,14 +720,36 @@ static Vec4IntResult SOFTRAST_CALL SampleLinearLevel(float s, float t, const u8
const Vec4<int> u = GetTexelCoordinatesQuadS(texlevel, s, frac_u, samplerID);
const Vec4<int> v = GetTexelCoordinatesQuadT(texlevel, t, frac_v, samplerID);
Nearest4 c = SampleNearest<4>(u.AsArray(), v.AsArray(), tptr[0], bufw[0], texlevel, samplerID);

#ifdef _M_SSE
__m128i zero = _mm_setzero_si128();
__m128i samples = _mm_loadu_si128((const __m128i*)(c.v));
__m128i top = _mm_unpacklo_epi8(samples, zero);
__m128i bot = _mm_unpackhi_epi8(samples, zero);
// I just a want reasonably efficient
// __m128i mul_u = _mm_setr_epi16(0x10 - frac_u, 0x10 - frac_u, 0x10 - frac_u, 0x10 - frac_u, frac_u, frac_u, frac_u, frac_u);
// GCC/clang do something decent for that, MSVC - not so much.
// Hence this. (0x10 - frac_u) is expressed as (frac_u ^ 0xF) + 1,
// which REQUIRES 0 <= frac_u < 0x10.
__m128i mul_u = _mm_set1_epi16(frac_u);
mul_u = _mm_xor_si128(mul_u, _mm_setr_epi16(0xF, 0xF, 0xF, 0xF, 0x0, 0x0, 0x0, 0x0));
mul_u = _mm_add_epi16(mul_u, _mm_setr_epi16(0x1, 0x1, 0x1, 0x1, 0x0, 0x0, 0x0, 0x0));
top = _mm_mullo_epi16(top, _mm_set1_epi16(0x10 - frac_v));
bot = _mm_mullo_epi16(bot, _mm_set1_epi16(frac_v));
__m128i sum = _mm_add_epi16(top, bot);
sum = _mm_mullo_epi16(sum, mul_u);
sum = _mm_add_epi16(sum, _mm_shuffle_epi32(sum, _MM_SHUFFLE(3, 2, 3, 2)));
sum = _mm_srli_epi16(sum, 8);
sum = _mm_unpacklo_epi16(sum, zero);
return sum;
#else
Vec4<int> texcolor_tl = Vec4<int>::FromRGBA(c.v[0]);
Vec4<int> texcolor_tr = Vec4<int>::FromRGBA(c.v[1]);
Vec4<int> texcolor_bl = Vec4<int>::FromRGBA(c.v[2]);
Vec4<int> texcolor_br = Vec4<int>::FromRGBA(c.v[3]);
Vec4<int> top = texcolor_tl * (0x10 - frac_u) + texcolor_tr * frac_u;
Vec4<int> bot = texcolor_bl * (0x10 - frac_u) + texcolor_br * frac_u;
return ToVec4IntResult((top * (0x10 - frac_v) + bot * frac_v) / (16 * 16));
#endif
}

static Vec4IntResult SOFTRAST_CALL SampleLinear(float s, float t, Vec4IntArg prim_color, const u8 *const *tptr, const uint16_t *bufw, int texlevel, int levelFrac, const SamplerID &samplerID) {
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